How do you justify your justifications?

The regress argument (also known as the diallelus^[1] (Latin) or diallelon, from Greek di allelon "through or by means of one another")) is a problem in epistemology and, in general, a problem in any situation where a statement has to be justified.^[2][3][4]

According to this argument, any proposition requires a justification. However, any justification itself requires support. This means that any proposition whatsoever can be endlessly (infinitely) questioned

The argument is usually attributed to Sextus Empiricus, and has been restated by Agrippa as part of what has become known as "Agrippa's trilemma". The argument can be seen as a response to the suggestion in Plato's Theaetetus that knowledge is justified true belief.

Structure[edit]

Assuming that knowledge is justified true belief, then:

1. Suppose that P is some piece of knowledge. Then P is a justified true belief.
2. The only thing that can justify P is another statement – let's call it P₁; so P₁ justifies P.
3. But if P₁ is to be a satisfactory justification for P, then we must know that P₁.
4. But for P₁ to be known, it must also be a justified true belief.
5. That justification will be another statement - let's call it P₂; so P₂ justifies P₁.
6. But if P₂ is to be a satisfactory justification for P₁, then we must know that P₂ is true
7. But for P₂ to count as knowledge, it must itself be a justified true belief.
8. That justification will in turn be another statement - let's call it P₃; so P₃ justifies P₂.
9. and so on, ad infinitum.